Rotary kiln apparatus with suspension preheater having burner for calcining

ABSTRACT

The apparatus consists of a suspension preheater with a calcining burner, a rotary kiln, a planetary type multicylinder precooler installed into a unitary construction with the rotary kiln and a main cooler and it aims to take away many problems and defects caused by the conventional system having production capacity more than several thousand tons per day.

O United States Patent 1 1 1111 3,891,383 Kobayashi June 24, 1975 [54]ROTARY KILN APPARATUS WITH 3,358,977 12/1967 Jensen 432/80 SUSPENSIONPREHEATER HAVING g l 52 1m1zu e a. BURNER FOR CALCINING 3,539,16411/1970 Brachthauser 432/80 [75] Inventor: Toshihiro Kobayashi, Tokyo,Japan 3,612,499 10/1971 Weber 432/80 3,723,597 3/1973 Dambrine et311...... 431/61 Asslgneei lShlkaWaJlma-Harlma Jukogyo 3,782,888 1 1974Cnare 432 14 Kabushiki Kaisha, Tokyo, Japan Filedl Dec. 1973 PrimaryExaminer-John J Camby Assistant Examiner-Hem C. Yuen 21 A 1. N .1421,329 y 1 pp 0 Attorney, Agent, or FirmScr1vener Parker Scr1vener &Clarke [30] Foreign Application Priority Data Dec. 6, 1972 Japan47-12164 [57] ABSTRACT The apparatus consists of a suspension preheaterwith [58] H "432/lO5 6 82 l 17 a calcining burner, a rotary kiln, aplanetary type mule 432/8O 133 l5 ticylinder precooler installed into aunitary construc- 172, 5 6 tion with the rotary kiln and a main coolerand it aims to take away many problems and defects caused by theconventional system having production capacity [56] g gf il'gg gzf morethan several thousand tons per day.

3,350,077 10/1967 3 Claims, 3 Drawing Figures Christensen 432/80PATENTEI] JUN 24 I975 SHEET PATENTEDJUN24 197s SHEET 2 TEMPERATU RE IIOOzoo PRE- COOLER MAIN COOLER RESIDENCE TIME INDEX 1 ROTARY KILN APPARATUSWITH SUSPENSION PREHEATER HAVING BURNER FOR CALCINING The presentinvention relates to a large capacity rotary kiln apparatus with asuspension preheater in which a secondary burner or burners (hereaftercalled a calcining burner) is installed.

In order to burn raw materials in the form of powder, expecially that ofportland cement clinker, an installation consisting of a combination ofa rotary kiln with a suspension preheater (hereafter called SP kiln orSP apparatus) and a grate type cooler had been employed because itsthermal efficiency is high and a large production capacity could beeasily obtained by one unit. Recently there has been devised anddemonstrated a rotary kiln with a suspension preheater in which acalcining burner is installed and the endothermic reaction of rawmaterials is substantially accomplished hereafter called SCP kiln or SCPapparatus so that the burning through-put of the rotary kiln may bedoubled in comparison with the conventional SP kilns. In general thebigger the size of rotary kilns becomes, the shorter the service life ofrefractory materials considerably, but the SCP apparatus makes itpossible to double the production with a same rotary kiln in size whichhad been used for SP kilns.

However the conventional SCP apparatus with a grate cooler still havemany problems and defects, expecially on the clinker cooler and theheight of apparatus as the production capacity being increased.

One of the objects of the present invention is therefore to provide animproved SCP kiln which may substantially eliminate the problems anddefects encountered in the conventional SCP kilns.

The objects, features and advantages of the present invention willbecome more apparent from the following description of one preferredembodiment thereof taken in conjunction with the accompanying drawing.

FIG. 1 is a diagrammatic view partly in sectionof a conventional SCPkiln;

FIG. 2 is a diagrammatic view, partly in section, of a rotary kilninstallation in accordance with the present invention; and

FIG. 3 is a graph illustrating the clinker cooling speeds attained bythe kiln installation shown in FIGS. 1 and 2.

Same reference numerals are used to designate similar parts throughoutthe figures.

Prior to the description of the preferred embodiment of the presentinvention, a conventional SCP apparatus with a clinker cooler will bedescribed briefly in order to distinctly point out the problems anddefects thereof. Raw materials charged into a suspension preheater 1from a feed port I of the uppermost stage is heated by highertemperature gas as they flow down from one stage to the next. To acalcining burner 5 installed at the lowermost stage of the suspensionpreheater is'supplied a high temperature combusion air induced from aclinker cooler 3 through a secondary air duct 82. -As

a result the endothermic reaction of raw materials is substantiallycompletely accomplished whereas in the conventional SP apparatus thereaction takes place about 40% in the preheater. Thereafter rawmaterials are sent to a rotary kiln 2 and burnt to cement clinker whichis then descharged upon a grate 6 in the grate type clinker cooler 3.While clinker is transported toward the discharge end II by thereciplocate movement of the grate 6, it is cooled by cooling air whichis sent by a blower 7 so as to pass through the clinker bed from theunder side of the grate 6 of the cooling air which has been heated up bythe clinker, the highest temperature air is induced into the rotary kiln2 through the hood connecting the cooler with the kiln as combustion airof a kiln burner 4, and the next highest temperature air is induced tothe suspension preheater 1 through a vent port 8 as combustion air ofthe calcining burner 5 by way of a dust collector 81 for clinker dustremoval and the secondary air duct 82. The remaining air is dischargedthrough a vent 9 of the clinker cooler 3 to the atmosphere after it hasbeen treated by a dust collector (not shown).

In the conventional apparatus air velocity in the secondary air duct isgenerally higher than gas velocity in the kiln from the economicalreasons and in addition the dust collector 81 is installed so that thesecondary air flow system needs higher draft resistance than the kilngas flow system. The kiln gas flow system of the suspension preheater lis provided with an orifice 83 (a narrowed gas passage) so as to keepbalance of the draft between two flow systems. In place of the orifice afan may be installed in the secondary air duct 82 but it is not apractical method in view of its durability because a high temperatureair with some clinker dust has to be handled. The clinker dust caught bythe collector 81 is returned to cooler 3.

In the SCP apparatus of the type described, even when it is of a verylarge size, the service life of the refractory materials can beelongated so that the apparatus may be operated continuously for a longperiod of time because the thermal load of the rotary kiln may beconsiderably reduced due to the effects of the calcining burner in thepreheater as compared with the conventional SP kilns. However in thegrate type clinker cooler of a large size unit the impact of clinkerbeing dropped from the rotary kiln and the thermal load are increased.Therefore the wear and abrasion of the grate at the high temperatureportion thereof are remarkably increased. The width of the grate cannotbe increased in proportion to the capacity of the rotary kiln because ifit is increased the formation of clinker bed the grate is adverselyaffected. On the other hand the speed of the grate cannot be alsoincreased in proportion to the capacity because the abrasion and wear ofthe grate are much enhanced. As a result the thickness of the clinkerlayer upon the grate must be increased gradually according to theenlargement of the size of the apparatus so that the power consumptionof the blower for cooling air is increased due to a pressure loss ofthicker clinker layer or bed.

Therefore the decrease of durability of a grate cooler, especially ofits grate plates, presents a very serious problem when the capacity ofthe apparatus must be increased. A planetary type multicylinder cooleris of greater advantage to the durability, but all air which is used forcooling the clinker must be induced into a kiln from the constructionview point so that it is not applicable for the SCP apparatus of thetype described hereinbefore. Furthermore a planetary type multicylindercooler is inferior in rapid and complete cooling effects of clinker to agrate type cooler. Moreover in the conventional SCP apparatus theorifice must be installed in the kiln gas flow system as describedherein before so as to keep balance of the draft between two flowsystems and it is indispensable that the power consumption of theapparatus is increased regardless of the orifice.

In view of the above the primary object of the present invention is toprovide a SCP apparatus with a cooler which may substantially eliminatethe problems and defects encountered in the conventional apparatus andwhich may serve to increase the capacity of the apparatus and todecrease the height thereof. Briefly stated the apparatus of the presentinvention is characterized by a planetary type multicylinder precoolerassembled into a unitary construction with a rotary kiln so thatcombustion air required by a kiln burner is induced through thecylinders of said precooler and that when the cylinders of saidprecooler pass the heighest point, clinker in the cylinders isdischarged to a main cooler.

According to one preferred embodiment of the present invention, betweenthe precooler and the hot end of the main cooler is interposed aninclined surface for charging clinker and/or a clinker pocket, and therotary kiln and the main cooler are disposed horizontally and in series.

The apparatus of the present invention shown in FIG. 2 is similar to theconventional apparatus shown in FIG. 1 except that high temperatureclinker is cooled by a planetary type multicylinder precooler 31assembled into a unitary construction with the rotary kiln 2 and a maincooler 32 joined to the planetary type multicylinder precooler 31.Combustion air of ambient tempera ture and of the quantity required forthe combustion of a rotary kiln burner 4 is induced through thecylinders 'of the planetary type multicylinder precooler 31 so that hightemperature clinker in each cylinder is rapidly cooled or quenchedbefore it is discharged into the main cooler 32. In the main cooler 32which is of the grate type, clinker is completely cooled, and preheatedair of the quantity required for the combustion ofa calcining burner 5is induced through the dust collector 81 and the secondary air duct 82into the suspension preheater 1 so as to improve its thermal efficiency.Of cooling air sent from the blower 7 to the main cooler 32, theremaining air is discharged to the atmosphere through the vent 9 and thedust collector (not shown).

Next the mode of operation of the apparatus of the present inventionwill be described in more detail hereinafter. Assuming that the ratio ofthe fuel oil to be supplied to the rotary kiln burner 4 and thecalcining burner 5 of the suspension preheater l is 4 6, and clinkerdischarge from the rotary kiln 2 into the precooler 31 at thetemperature of about 1,300C, the clinker is cooled rapidly by air ofambient temperature, lets say C, induced into the cylinders of theprecooler 31 due to the draft of the rotary kiln 2 at a rate of 0.3 Nm/kg of clinker. Thus clinker may be cooled to 900C before it wasdischarged into the main cooler 32, whereas combustion air preheated toabout 900C may be induced into the rotary kiln 2. Clinker dischargedinto the grate type main cooler 32 from the precooler 31 may be cooledcompletely to about 60C by cooling air of ambient temperature suppliedat a rate of about 2.4 Nm lkg of clinker, whereas combustion airpreheated to about 600C may be induced through the second air duct 82into the suspension preheater 1 at a rate of 0.6 Nm' /kg of clinker, andthe remaining air of about 190C may be discharged through the vent 9 ata rate of 1.8 Nm /kg of clinker.

It is generally required that clinker discharged from a rotary kiln israpidly cooled to 1,000C in order to obtain clinker of better quality.In a planetary type multicylinder cooler provided with a conventional SPkiln, the cooling speed of clinker is shown by the curve a in FIG. 3when clinker is cooled by cooling air at a rate of 0.9 Nm /kg ofclinker, whereas the air is preheated as indicated by the curve d inFIG. 3. In case of grate cooler operated by cooling air at a rate ofabout 2.7 Nm /kg of clinker the cooling speed is shown by the curve I)in FIG. 3. It is clear that the clinker is cooled more rapidly andcompletely by a grate cooler than by a planetary type multicylindercooler.

According to the present invention, high temperature clinker is rapidlycooled in the planetary type multicylinder precooler along the coolingcurve c between the points A and B in FIG. 3 so that the dischargedclinker may be cooled to 900C. On the other hand combustion air for akiln burner may be preheated along the curve e. Therefore it is seenthat the rapid coding efficiency of the planetary type multicylinderprecooler of the present invention is substantially similar to that of agrate cooler. Furthermore according to the present invention the clinkercharged to the main cooler is further cooled along the curve I; from thepoint B to the point C where temperature may be about 60C.

Next the construction of the apparatus of the present invention will bedescribed in more detail hereinafter. Since clinker is rapidly cooled to900C by the planetary type multicylinder precooler, which is constructedwith no consumable part such as a grate, before it is charged to thegrate type main cooler, the thermal load of the main cooler isremarkably reduced.

There has been devised and demonstrated an inclined charging surfacedisposed at the hot end of the grate coolerin order to prevent the gratefrom being directly exposed to the impact of the clinker discharged fromthe rotary kiln and also to facilitate the formation of a bed or layerof clinker on the grate. However in practice clinker discharged from thekiln is in liquid phase partially so that it adheres to and grows on theinclined surface thus causing troubles. However in the apparatus of thepresent invention clinker, which'is to be discharged into the maincooler 32, is rapidly cooled by the precooler 31 to at least less than1,000C at which temperature clinker is already on solid phase at itssurface and has no adhesive nature. Therefore an inclined surface 10and/or a clinker pocket 11 can be disposed at the hot end of the maincooler 32 without difficulties in order to absorb the impact of clinkercharged onto the grate and at the same time to uniformly spread clinkerover the whole width of the grate, thereby forming a desired bed orlayer of clinker.

According to the present invention a weir 12 is disposed at thedischarged end of each cylinder so that clinker in each cylinder isdischarged from the precooler 31 into the main cooler 32 at the highestposition of the cylinder, that is the vertex of the rotation of thecylinder, and the main cooler 32 is installed substanitally inhorizontal relation with the rotary kiln 2 and the precooler 31 so thatthe overall height of the apparatus may be decreased by about 10m incomparison with the conventional apparatus of the-type shown in FIG. 1.

Furthermore in comparison with the conventional planetary typemulticylinder cooler of the SP kilns, the average temperature differencebetween clinker and cooling air becomes 1.5 times and the heat capacityto be exchanged in the cooler is only about 40% because clinker iscooled from about 1,300C to about 900C by air of ambient temperature inthe planetary type multicylinder precooler in accordance with theapparatus of the present invention. As a result the size of the coolermay be reduced from /3 to so that even when the capacity of theapparatus is increased the precooler may be installed in a cantilevermanner upon the discharge end of an extended shell of the rotary kilnwithout any additional support.

Next the electric power consumption will be ex-' plained. In generalcooling air is sent into a grate type cooler with forced draft so as topass through a bed of clinker. Therefore by the grate cooler havingcapacity of I 150 tons clinker per hour the power consumption of theblower may be 5 KWH/t of clinker which is considerably greater ascompared with other coolers. Furthermore the higher the temperature ofclinker, the higher the permeable resistance of the clinker bed or layerbecomes. However according to the present invention clinker of a hightemperature zone is rapidly cooled in the planetary type multicylinderprecooler whose draft resistance is very small and the draft resistanceof the precooler which must be added to the kiln gas flow system may bewell covered by the delation of a said orifice which has been installedregardlessly in the preheater of the conventional SPC apparatus.Therefore the precooler of the present invention does not bring anyadditional power consumption. In comparison with the conventionalapparatus with a grate type cooler of a capacity mentioned above, thepower consumption of the blower for cooling air in the present inventionmay be reduced to 1.5 KWI-I/t of clinker.

In the conventional grate cooler provided with the conventional SP orSCI kiln installation, the greater the capacity of the rotary kiln, thegreater the thickness of the clinker bed or layer or the grate becomesas de' scribed hereinbefore. However in the installation of the presentinvention the sloped surface and/or the clinker pocket 11 is so arrangedas to prevent the grate from being exposed to the impact of clinker andto facilitate the uniform distribution of clinker over the grate.Therefore the thickness of the clinker bed or layer will not beincreased as the capacity of apparatus being enlarged. As a result thepower consumption of the blower may be saved by the apparatus of thepresent invention as much as 2.0 KWH/t of clinker in case of theinstallation of a large capacity.

Furthermore when it is not required to cool clinker to a temperature ofless than 100C, a double pass method can be applied for the main cooleras a preferred embodiment of the present invention. In this case thecooler chamber above the grate is divided into two zones, i.e. a highand a low temperature zones, and cooling air is supplied to respectivezones by two independent fans. Cooling air supplied to the lowtemperature zone is vented from a vent port and sent to the suction sideof the cooling air fan for the high temperature zone by way of a dustcollector. Thus clinker of high temperature zone is cooled by vent airfrom the low temperature zone. By the double pass method, a heatrecuperative efficiency is raised and air polusion caused by wastingvent air can be solved completely, so it had been deviced anddemonstrated also by the conventional SP kilns but it was not practicalbecause the grate at the high temperature zone had been overheated andservice life of the grate had been shortened remarkably. In the presentinvention, however, clinker which is cooled to about 900C by theprecooler is supplied to the main cooler so that the grate will not benated. When the double pass method of the grate type cooler or thecounter flow rotary cooler is used as the preferred embodiment of thepresent invention the effects, herein mentioned, such as mitigation ofthermal load of the main cooler, the overall height of the apparatus,etc. may be fully achieved.

The features and advantages of the present invention may be summaried asfollows:

1. The planetary type multicylinder precooler, which is installed into aunitary construction with the rotary kiln, may rapidly cool clinkerbelow 1000C only by air which is used as preheated combustion air forthe rotary kiln. The precooler is simple in construction and adapted tobe used with a rotary kiln installation of a large capacity.

2. The inclined surface and/or the clinker pocket are provided at thehot end of the main cooler so as to prevent the grate from beingdirectly exposed to the impact of clinker and also to facilitate theuniform distribution of clinker over the whole width of the grate.Furthermore the thermal load of the main cooler is reduced because ofthe installation of the precooler. As a result the durability of thegrate type main cooler is not lowered even when the capacity of therotary kiln installation is increased.

3. The weir is attached to the discharge end of the precooler so thatclinker may be discharged into the main cooler only when each cylinderof the precooler reaches the highest position or the vertex of therotation. Therefore the rotary kiln and the main cooler may be installedhorizontally and in series so that the overall height of the rotary kilninstallation of the present invention may be reduced by about 10 metersas compared with the conventional installation.

4. Since the average temperature difference between clinker and coolingair in the precooler is large and the quantity of heat exchange is less,the precooler may be mounted upon the discharge end of the extendedshell of the rotary kiln in a cantilever manner. Therefore opposed tothe planetary type multicylinder cooler used in the conventional SPkilns of a large capacity it is not required to provide any support forthe precooler.

5. Clinker of high temperature whose permeable resistance is high israpidly cooled in the planetary type precooler, so that even when thegrate type main cooler is employed the economy of the power consumptionof 1.5 2 KWI-I/t of clinker may be attained.

6. When it is not required to cool clinker to a temperature of less thanC, a double pass method of the grate type cooler or a counter flowrotary cooler can be applied so as to improve the heat recuperativeefficiency and to eliminate the wasting of cooler vent air.

Thus the present invention may provide a SCP rotary kiln installationwith precooler which may eliminate the problems and defects encounteredin the conventional installations when its capacity must be increasedand which may decrease the overall height thereof.

What is claimed is: t

1. Apparatus of the type having a suspension preheater to which powderyraw materials are supplied and also having a calcining burner, a rotarykiln for receiving the raw materials and including a burner for burningthe raw materials to cement clinker and also including a discharge endfor the clinker, and a planetary type multicylinder precooler associatedwith said discharge end comprising a plurality of cylinders arranged ina circle concentric with the kiln, said cylinders extending parallel tothe kiln longitudinal axis and having means at its outlet ends toprovide direct communication'with the atmosphere and having its inletends communicating with said discharge end, the outlet ends of eachcylinder being provided with an upstanding weir means arranged to allowdischarge of clinker only when the cylinders approach the highestposition of rotation and a main cooler having an inlet for receivingclinker from the outlet ends of the cylinders and a vent port connectedwith the calcining burner.

2. Apparatus as set forth in claim 1 wherein an inclined surface and aclinker pocket are arranged at the inlet of the main cooler.

3. Apparatus as set forth in claim 2 wherein the rotary kiln and maincooler are arranged horizontally and in series and clinker is dischargedinto the main cooler when each cylinder of the precooler passes thehighest position of rotation.

1. Apparatus of the type having a suspension preheater to which powderyraw materials are supplied and also having a calcining burner, a rotarykiln for receiving the raw materials and including a burner for burningthe raw materials to cement clinker and also including a discharge endfor the clinker, and a planetary type multicylinder precooler associatedwith said discharge end comprising a plurality of cylinders arranged ina circle concentric with the kiln, said cylinders extending parallel tothe kiln longitudinal axis and having means at its outlet ends toprovide direct communication with the atmosphere and having its inletends communicating with said discharge end, the outlet ends of eachcylinder being provided with an upstanding weir means arranged to allowdischarge of clinker only when the cylinders approach the highestposition of rotation and a main cooler having an inlet for receivingclinker from the outlet ends of the cylinders and a vent port connectedwith the calcining burner.
 2. Apparatus as set forth in claim 1 whereinan inclined surface and a clinker pocket are arranged at the inlet ofthe main cooler.
 3. Apparatus as set forth in claim 2 wherein the rotarykiln and main cooler are arranged horizontally and in series and clinkeris discharged into the main cooler when each cylinder of the precoolerpasses the highest position of rotation.